1) In 1840, Pope Gregory XVI established the Diocese of California to encompass what is now the U.S. states of California, Arizona, Nevada, Utah, western Colorado and southwest Wyoming Baja California in Mexico.
2) In 1849, the Diocese of Monterey resulted from a split between the American portion of the Diocese of California in the north and the Mexican portion of the diocese to the south. The American portion was named Diocese of Monterey and encompassed all of American California, Nevada and Utah. Later, in 1953, much of northern California, Nevada and Utah split from the Diocese of Monterey to form the Diocese of San Francisco.
3) In 1859, recognizing the rising importance of Los Angeles versus that of Monterey, Bishop Amat convinced the Holy See to move the see to Los Angeles and have it renamed Diocese of Monterey-Los Angeles.
4) In 1936, the Diocese of Los Angeles & San Diego split to form the Diocese of San Diego and today's Archdiocese of Los Angeles. Pope Pius XI elevated Bishop Cantwell to be the new Archbishop of Los Angeles.
5) In 1953, Pope Pius XII elevated Archbishop McIntyre to become the first cardinal in the Western United States.
6) In 2002, the present-day Cathedral of Our Lady of the Angels was opened as the new mother church of the Archdioces of Los Angeles.

Bishop Amat moved the seat of the Monterey-Los Angeles Diocese to Los Angeles in 1859. It was under his oversight that, in 1876, St. Vibiana Cathedral was built.

Archbishop John J. Cantwell served as head of the Los Angeles Archdiocese for 30 years, longer than any in his succession. The Los Angeles diocese was elevated to an Archdiocese and Bishop Cantwell to Archbishop in 1936.

Archbishop J. Francis McIntyre was appointed by Pope Pius XII in 1952 to become the first Cardinal in the western United States.

Cardinal Roger M. Mahony was the first head of the Los Angeles Archdiocese to have been born in Los Angeles.

Archbishop Gómez is the first Hispanic to serve as Archbishop of Los Angeles.